1. Field of the Invention
The present invention relates to an image recorder that records image on a recording material such as a printing plate and photosensitive film. In particular, the invention relates to an image recorder having more than one recording head for recording image.
2. Description of the Background Art
There is known an image recorder that records image on a printing plate based on an image data, which is called “CTP (computer to plate) device.” In the most widespread type of this CTP device, with a printing plate mounted on a drum, a secondary scanning of a recording head in an axial direction of the drum is performed while the drum is rotated in a primary scanning direction, thereby recording image in spiral form with respect to the peripheral surface of the drum. This image recorder aims at increasing the recording rate of the image recorder as a whole, by using a recording head of a multibeam type in which plural beam columns are disposed. However, the above spiral recording system is unsatisfactory due to the problem that the tilting of image recorded in spiral is increased as the number of beam columns is increased.
To solve this problem, there is known a technique of increasing recording rate by arranging such that plural recording heads for recording images perform concurrent scanning over plural areas on a printing plate. In this conventional image recorder, plural recording heads are disposed in a secondary scanning direction so that the individual recording heads record image concurrently.
However, when an image is divided and recorded by the plural recording heads as described above, it is difficult to maintain continuity at a joint between the recording heads. Although in the conventional image recorder, a spot position of each recording head is detected to correct an irradiation position, a slight line unevenness etc. might occur because of difficulties in attaining a complete correction, which can deteriorate printing quality.